1. Field of the Invention
The present invention relates to a protection layer of a PDP (Plasma Display Panel) and a method of forming the same and, more particularly, to a protection layer of a PDP and a method of forming the same by which an excellent protection layer can be formed on the surface of the PDP's substrate.
2. Discussion of Related Art
FIG. 1 is a cross section of a general PDP. As shown in FIG. 1, the PDP comprises: an upper structure having a pair of upper electrodes 4 formed on the same surface of a front glass substrate 1, a dielectric layer 2 formed on the upper electrodes 4 by printing method, and a thin film 3 (hereinafter, referred to as protection layer) deposited on the dielectric layer 2; a lower structure having lower electrodes 12 formed on a back glass substrate 11, a barrier rib 6 formed to prevent a mis-discharge in the cell adjacent to the lower electrodes, and phosphor 8, 9 and 10 formed around the barrier rib 6 and the lower electrodes 12; and a discharging region 5 formed in a space between the upper and lower structures by injecting an inert gas therein.
The lower electrodes 12 are termed "data electrodes" into which image data is transferred. The upper electrodes 4 are termed "display electrodes" comprising a scan electrode for discharging the image data fed into the cell, and a sustain electrode to maintain the cell's discharging.
The PDPs as constructed above are widely used as a flat display device because they can display signals at high speed and be manufactured in a large size.
Referring to FIG. 1, when an image data is transferred into the lower electrodes 12 and a discharging signal is fed into the scan electrode of the upper electrodes, a driving voltage is applied to the discharging space between the upper and lower electrodes, creating a surface discharge in the discharging region 5 on the surfaces of the dielectric and protection layers 2 and 3. Such a surface discharge causes ultraviolet radiation while the signal is entered.
Because the ultraviolet radiation does not last long enough to display signals, the discharging and sustain signals respectively applied by the scan and sustain electrodes of the upper electrodes 4 provide extra discharging time for a display while no image data is entered through the lower electrodes 12.
The ultraviolet ray 7 excites the phosphor 8, 9 and 10 to display color signals.
Electrons in the discharging cell are accelerated towards the negative (-) electrode by a driving voltage applied, colliding with a penning mixture gas consisting of mainly inert gases, i.e., He and additional Xe, Ne, or other gases. Thus excited inert gas generates the ultraviolet ray 7 having the wavelength of 147 nm. The ultraviolet ray 7 collides with the phosphor 8, 9 and 10 that surround the lower electrodes 12 and the barrier rib 6, to generate a light in the ultraviolet spectrum region.
PDPs must have the protection layer 3 on the whole surface of the dielectric layer to protect the dielectric layer 2 against sputtering effect caused by a secondary emission during a discharge, the protection layer 3 usually being a transparent layer consisting of magnesium oxide (hereinafter, referred to as MgO). The protection layer 3 protects the dielectric layer 2 of the cells to extend the life of the panel and reduce the driving voltages.
A conventional method of forming the protection layer 3 is disclosed in SID 94 DIGEST (P 323-326, by Amano), by which a MgO paste is prepared from MgO powder mixture in a solvent, screen printed to form an MgO protection layer 2 .mu.m thick and heated at 500.degree. C.
Such a screen printing can be performed at low costs for materials and available as an alternative new technique. It is applicable to MgO deposition on a glass substrate of an AC PDP but not appropriate in a difficult deposition of a MgO thick layer due to the PDP's characteristics.
As disclosed in European Patent Application No. 93400201.5(Publication No. EP0554172A1), a Mgo protection layer of several hundreds of nanometers in thickness might be coated by a vacuum method. The vacuum method is an E-beam and RF (Radio Frequency) sputtering that is expensive and inefficient in productivity due to its complex process such as vacuum and heat treatment. In addition, there are other limitations associated with the vacuum method, including firing voltage reduction and prevention of ion collisions to increase the device's life during a sputtering.